Kaguya-sama wo Kataritai is your typical extra fluff to complement your enjoyment of the main series, Kaguya-sama wa Kokurasetai: Tensai-tachi no Renai Zunousen.
The spin-off follows the shenanigans of Erika and Karen of the Mass Media Club as they fantasize about the main series' two leads, Kaguya Shinomiya and Miyuki Shirogane. Although the premise does seem simplistic, this episodic format allows the spin-off to build inside jokes and references that the main series utilizes as Easter eggs. Additionally, besides contributing small gags to the main series, Kaguya-sama wo Kataritai also provides an outsider's naive perspective of the events of Kaguya-sama wa Kokurasetai through Erika and
Karen. This builds some amusing dramatic irony as you watch misunderstandings snowball into pure delusion on the part of our two idiotic Mass Media Club members. Thus if you need a main reason to read this, you'd pick this up for some silly humor and to potentially find some more quirks in the main series.
The art is a simplistic imitation of the art of the main series, so do not expected to be blown away. The characters transition well from the main series to the spin-off, so there are no glaring inconsistencies between the two works, although the 4-koma format makes all the characters seem one dimensional in each chapter. Since it is episodic, there are very marginal plot developments throughout the spin-off, and you can even argue that due to the comedic style, the characters are completely stagnant or even regressing (but that isn't really a big issue). I would heavily advise you not to binge read this, rather you should pick this up when you have a couple minutes to kill or in need of a quick laugh.
At the end of the day, comedy is subjective. I found Kaguya-sama wo Kataritai to be funny relatively consistently. I cannot guarantee that you will find this just as funny as I did, but you will get an idea of how the spin-off suits your tastes by giving the first three or so chapters a read.